18181 has 2 divisors, whose sum is σ = 18182. Its totient is φ = 18180.

The previous prime is 18169. The next prime is 18191.

18181 is nontrivially palindromic in base 10.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 17956 + 225 = 134^2 + 15^2 .

It is a palprime.

It is a cyclic number.

It is not a de Polignac number, because 18181 - 2⁵ = 18149 is a prime.

It is a super-2 number, since 2×18181² = 661097522, which contains 22 as substring.

It is an alternating number because its digits alternate between odd and even.

18181 is a strobogrammatic number because it is the same when read upside-down.

18181 is an undulating number in base 10.

18181 is a lucky number.

It is a nialpdrome in base 12.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (18121) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 9090 + 9091.

It is an arithmetic number, because the mean of its divisors is an integer number (9091).

2¹⁸¹⁸¹ is an apocalyptic number.

It is an amenable number.

18181 is a deficient number, since it is larger than the sum of its proper divisors (1).

18181 is an equidigital number, since it uses as much as digits as its factorization.

18181 is an evil number, because the sum of its binary digits is even.

The product of its digits is 64, while the sum is 19.

The square root of 18181 is about 134.8369385591. The cubic root of 18181 is about 26.2949645070.

It can be divided in two parts, 181 and 81, that added together give a palindrome (262).

The spelling of 18181 in words is "eighteen thousand, one hundred eighty-one".